Simple
You've taken a seemingly simple design and added a few features to it. While a lot of other game makers could of been lazy and just left it to a simple point and click, you've gone a step further to make it less repetitive, good job.
I like the track of score, really builds up a level of competitiveness in the game, even if it's just against myself. I enjoy the implementation of health, a lot of games like this are very harsh in the sense that it's one hit one kill, you've gone out of your way to give us a chance to fight of the swarm, and closer enemies.
The visuals are very, very simple. But with a game like this they don't need to be so special. Maybe a background to play on would be nice? But I understand a blank background would mean players wouldn't get distracted as often.
It's a fun way to kill time, the only real downside to this I could see would be the constant barrage of advertisements. Other than that, good work.